Rotary dampers are commonly used with devices whose movement in one direction is sought to be controlled, typically by being slowed. For example, rotary dampers are used for door hinges, gate hinges, such as those in doors for pick-up truck beds, toilet seat hinges, piano key covers, and the like. These dampers are typically designed to be biased in a single rotational direction. Damping in this manner is commonly referred to as one-way or uni-directional damping.
This one-way damping facilitates strong damping in one rotational direction, such that movement of the object associated with the damper is slow and steady, avoiding any rapid, sudden or hard contacts, with surfaces, from rapid and uncontrolled movements. Accordingly, damping in the opposite rotational direction is minimal, allowing for rapid movement of the object associated with the damper.
This one-way biasing is a drawback should damping in the opposite direction be desired. Should some significant damping in the other direction be desired, the dampers must be made from two separate sets of molds and corresponding tooling. This is wasteful of time and materials.